Contour lines are lines drawn on a topographic map to indicate ground elevation or depression. They are a mix of straight and curved lines that enclose an area composed of points with the same value, either in terms of height or other parameters. Contour lines join points of equal and constant values, such as elevation, and have constant heights that are the same on each line in a topographic map. The vertical distance or difference in elevation between contour lines is called the contour interval. Widely separated contour lines indicate a gentle slope, while contour lines that are very close together indicate a steep slope.

Contour lines are critical to understanding the elevation profile of terrain or a particular land formation, and this information can be helpful when selecting a hiking route or lifesaving in a desperate survival situation. Beyond backpacking and hiking, countless other professions use them, such as land surveyors, foresters, engineers, miners, geologists, and hunters.

In cartography, contour lines are used to illustrate topographic maps, which show valleys and hills, and the steepness or gentleness of slopes. The configuration of these contours allows map readers to infer the relative gradient of a parameter and estimate that parameter at specific places. Contour lines tend to enclose the smallest areas on ridge tops, which are often narrow or very limited in spatial extent, and sharp contour points indicate pointed ridges.

In summary, contour lines are lines drawn on a topographic map to indicate ground elevation or depression, and they join points of equal and constant values, such as elevation. They are critical to understanding the elevation profile of terrain or a particular land formation and are used in various professions, such as land surveying, forestry, engineering, and geology.